MgCNi3 was discovered following on from the breakthrough of the finding of the MgB2 superconductor at the beginning of 200,which has subsequently been intensively studied; however, Jess attention has been paid to it due to its much lower superconducting transition temperature, Tc(TBk), as compared to that of MgB2f39k). But it has many interesting properties which need to be focused to obtain an understanding of its complicated physics. Energy band cotcuiotion shows that the density of state {DOS) at the Fermi level, N(EF)is dominated by Ni-d states and there is a van Hove singularity in the DOS just below EF(<S0-120 mev). MgCxNi3 has ~ simple cubic perovskite structure with space group pm-m and the lattice parameter, a ::: 3.812A for x=0.96 at ambient pressure and temperature. The carriers of MgCNi:J are of electron type in the normal state, although theoretically they were predicted to be· the hole type. Tc increases with increasing of x in MgCxNi3, but generally decreases with Ni site doping with transition metals such as Co, Mn, Fe, ! . Cu etc. Furthermore the Boron substitution induces disordered. 10% Born substitution at carbon site has decreased both the upper critical field (Hc2) and transition temperature {TC) on the ..• ,'-other ha.[ld, lower critical field slightly increases. Theoretically, DOS peak should be greatly reduced by doping at the Mg or Ni site, which accounts for the reduced TC. The transition critical · temf!erqture {TC) of MgCxNi3 is found to increase with increase of the external pressure (p) at a " the FJ,en~tratlon depth distinctly exhibits a non- s- wave BCS low temperature behavior type superconductors . - .. '· 'rate of dTC::: 0 . .015 k/k bars which .is one order lower than that of MgB2 and negative; and also . dp . .... .:» the pressure reduces the spin fluctuation, because the spin fluctuation and superconductivity are mutually competitive phenomena . rate of dTC::: 0 . .015 k/k bars which .is one order lower than that of MgB2 and negative; and also the pressure reduces the spin fluctuation, because the spin fluctuation and superconductivity are mutually competitive phenomena . rate of dTC::: 0 . .015 k/k bars which .is one order lower than that of MgB2 and negative; and also the pressure reduces the spin fluctuation, because the spin fluctuation and superconductivity are mutually competitive phenomena . Specific heat and tunneling spectroscopic measurements studies indicates that ans- waves BC ype weak or moderate coupling type II superconductors, but this needs further confirmations as the FJ,en~tratlon depth distinctly exhibits a non- s- wave BCS low temperature behavior type superconductors

IN PARTIAL FULFILLIMENT·OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN PHYSICS